Division 1.2 DEFINITIONS

Standard International (SI) units should be used in any case.

Test substance: any substance, whether the parent or relevant transformation products.

Transformation products: all substances resulting from biotic and abiotic transformation reactions of the test substance including CO₂ and bound residues.

Bound residues:”Bound residues” represent compounds in soil, plant or animal that persist in the matrix in the form of the parent substance or its metabolite(s) after extractions. The extraction method must not substantially change the compounds themselves or the structure of the matrix. The nature of the bond can be clarified in part by matrix-altering extraction methods and sophisticated analytical techniques. To date, for example, covalent ionic and sorptive bonds, as well as entrapments, have been identified in this way. In general, the formation of bound residues reduces the bioaccessibility and the bioavailability significantly (10) [modified from IUPAC 1984(11)].

Aerobic transformation: (oxidising): reactions occurring in the presence of molecular oxygen (12).

Anaerobic transformation: (reducing): reactions occurring under exclusion of molecular oxygen (12).

Natural waters: are surface waters obtained from ponds, rivers, streams, etc.

Sediment: is a mixture of mineral and organic chemical constituents, the latter containing compounds of high carbon and nitrogen content and of high molecular masses. It is deposited by natural water and forms an interface with that water.

Mineralisation: is the complete degradation of an organic compound to CO₂, H₂O under aerobic conditions, and CH₄, CO₂ and H₂O under anaerobic conditions. In the context of this test method, when radiolabelled compound is used, mineralisation means extensive degradation of a molecule during which a labelled carbon atom is oxidised or reduced quantitatively with release of the appropriate amount of ¹⁴CO₂ or ¹⁴CH₄, respectively.

Half-life, t_0.5, is the time taken for 50% transformation of a test substance when the transformation can be described by first-order kinetics; it is independent of the initial concentration.

DT₅₀ (Disappearance Time 50): is the time within which the initial concentration of the test substance is reduced by 50%.

DT₇₅ (Disappearance Time 75): is the time within which the initial concentration of the test substance is reduced by 75%.

DT₉₀ (Disappearance Time 90): is the time within which the initial concentration of the test substance is reduced by 90%.